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Shiv Nadar University

(SoNS) School of Natural Sciences

The phase behavior of the anionic surfactant sodium dodecyl sulfate (SDS) in the presence of the strongly binding counterion p-toluidine hydrochloride (PTHC) has been examined using small-angle X-ray diffraction and polarizing microscopy. A hexagonal-to-lamellar transition on varying the PTHC to SDS molar ratio (α) occurs through a nematic phase of rodlike micelles (N C) → isotropic (I) → nematic of disklike micelles (N D) at a fixed surfactant concentration (φ). The lamellar phase is found to coexist with an isotropic phase (I′) over a large region of the phase diagram. Deuterium nuclear magnetic resonance investigations of the phase behavior at φ = 0.4 confirm the transition from NC to N D on varying α. The viscoelastic and flow behaviors of the different phases were examined. A decrease in the steady shear viscosity across the different phases with increasing a suggests a decrease in the aspect ratio of the micellar aggregates. From the transient shear stress response of the NC and ND nematic phases in step shear experiments, they were characterized to be tumbling and flow aligning, respectively. Our studies reveal that by tuning the morphology of the surfactant micelles strongly binding counterions modify the phase behavior and rheological properties of concentrated surfactant solutions. © 2009 American Chemical Society.

Physics

World University root node

Langmuir

Re-entrant phase behavior of a concentrated anionic surfactant system with strongly binding counterions

We report on the effects of 2 MeV He+-ion irradiation on the magnetic and structural properties of Pt/Cr/Co multilayers. We observe He+-ion irradiation leads to mixing across the interfaces [Pt (2.5 nm)/Cr (0.8 nm)/Co (3.0 nm)] × 6/Si multilayers. In addition, we observe Co-Cr-Pt phase formation at the highest fluence of 5.5 × 1016 ions cm-2. This is accompanied by an enhancement in the coercivity. Such enhancement in the coercivity is attributed to inhomogeneous alloying and a possible mixing-induced strain. High-resolution transmission electron microscopy confirms the formation of CoCrPt ternary alloy phase. These findings are explained in the light of ion beam induced recoil mixing and ionization events. © 2009 Elsevier B.V. All rights reserved.

Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms

Modification of the magnetic and the structural properties of Pt/Cr/Co multilayers by He+-ion irradiation

Titanium(ii) solutions, prepared by dissolving titanium metal in triflic acid and HF, react readily with derivatives of Cr(vi), Cr(v) and Cr(iv). Reductions of Cr(vi) and Cr(iv), carried out with [Co(NH3) 5Br]2+ as a scavenger for Cr(ii), yield no detectable Co2+, indicating that 2e- steps, bypassing Cr(v) and Cr(iii), are not operative. Catalysis by Ti(iv) is observed only for reduction of Cr(vi). Rates for reduction by Ti(iii) are remarkably similar to those for the corresponding reductions by Ti(ii). The addition of Ti(iii) to triflic acid and HF results in rapid and quantitative disproportionation to Ti(ii) and Ti(iv). © 2009 The Royal Society of Chemistry.

Chemistry

Fulltext

Dalton Transactions

Reactions of aquatitanium(II) with hypervalent chromium species

The Journal of chemical physics

Large-scale correlated study of excited state absorptions in naphthalene and anthracene

Enzyme linked immunosorbent assay (ELISA) was used for the analysis of tetracycline, chlortetracycline, oxytetracycline, and their transformed compounds in environmental water samples. The antibodies employed in ELISA showed high relative affinity for tetracycline, epitetracycline, chlortetracycline, and epichlortetracycline as compared to anhydrotetracycline, epianhydrotetracycline, and anhydrochlortetracycline. The specificity and crossreactivity of these antibodies are discussed in relation to the electrostatic potentials and average local ionization energies computed on the molecular surfaces of tetracycline antibiotics and their transformed compounds with an objective of identifying common features as well as differences that may be related to the experimentally observed variation in cross-reactivity values. The computations were performed at both the HF/STO-3G and HF/6-31+G * levels using the Gaussian 98 program. The results in this study are based upon molecular electrostatic potentials and local ionization energies computed on isodensity molecular surfaces. The surface electrostatic potentials are characterized in terms of a group of statistically defined quantities, which include the average deviation, the positive, negative, and total variances, positive and negative surface extrema, and a parameter indicating the degree of electrostatic balance. © 2009 American Chemical Society.

Journal of Physical Chemistry A

Computational prediction of antibody binding sites on tetracycline antibiotics: Electrostatic potentials and average local ionization energies on molecular surfaces

Using combined electroluminescence (EL) and photoluminescence (PL) studies we establish that the energy transfer process from the Er3+ to the Ge-related oxygen-deficiency centers (GeODCs) plays the key role in enhancing the 404 nm EL intensity in Ge-rich SiO2. Er doping induced structural modification does not appear to be relevant, which is deduced from the 404 nm PL quenching with increasing Er concentration, implying a gradual loss of GeODCs. In contrast to PL, the 404 nm EL intensity increases by 0.3% Er doping followed by a gradual decrease in intensity for higher Er concentrations, which is described in terms of a competition between the energy transfer process and the gradual segregation of Er due to the destruction of GeODCs with Er doping. This fact is further discussed in the light of ab initio molecular orbital calculations. © 2009 American Institute of Physics.

Journal of Applied Physics

The role of Ge-related oxygen-deficiency centers in controlling the blue-violet photo- and electroluminescence in Ge-rich SiO2 via Er doping

Using combined microstructural and electroluminescence (EL) investigations of the Er-doped Ge-rich SiO2 layers, it is established that the Ge-related oxygen-deficiency centers (GeODCs), which are associated with the 407 nm light emission, are situated at the Ge nanocrystal/ SiO2 interface. Electrically driven energy transfer from the Er3+ to GeODCs causes an increase in the 407 nm EL intensity. It reaches a maximum before quenching with increasing Er concentration due to the crystalline-to-amorphous transition of Ge nanocrystals. Ge concentration dependent quenching of the maximum EL intensity and the peak shifting toward higher Er concentration are discussed in terms of the reduction of the surface-to-volume ratio with increasing nanocrystal size. © 2009 American Institute of Physics.

Defect-engineered blue-violet electroluminescence from Ge nanocrystal rich SiO2 layers by Er doping

The hepatitis E virus (HEV), a nonenveloped RNA virus, is the causative agent of hepatitis E. The mode by which HEV attaches to and enters into target cells for productive infection remains unidentified. Open reading frame 2 (ORF2) of HEV encodes its major capsid protein, pORF2, which is likely to have the determinants for virus attachment and entry. Using an ∼56-kDa recombinant pORF2 that can self-assemble as virus-like particles, we demonstrated that cell surface heparan sulfate proteoglycans (HSPGs), specifically syndecans, play a crucial role in the binding of pORF2 to Huh-7 liver cells. Removal of cell surface heparan sulfate by enzymatic (heparinase) or chemical (sodium chlorate) treatment of cells or competition with heparin, heparan sulfate, and their oversulfated derivatives caused a marked reduction in pORF2 binding to the cells. Syndecan-1 is the most abundant proteoglycan present on these cells and, hence, plays a key role in pORF2 binding. Specificity is likely to be dictated by well-defined sulfation patterns on syndecans. We show that pORF2 binds syndecans predominantly via 6-O sulfation, indicating that binding is not entirely due to random electrostatic interactions. Using an in vitro infection system, we also showed a marked reduction in HEV infection of heparinase-treated cells. Our results indicate that, analogous to some enveloped viruses, a nonenveloped virus like HEV may have also evolved to use HSPGs as cellular attachment receptors. Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Life Sciences

Journal of Virology

Heparan sulfate proteoglycans are required for cellular binding of the hepatitis E virus ORF2 capsid protein and for viral infection

The TIM23 complex is the major translocase of the mitochondrial inner membrane responsible for the import of essentially all matrix proteins and a number of inner membrane proteins. Tim23 and Tim50, two essential proteins of the complex, expose conserved domains into the intermembrane space that interact with each other. Here, we describe in vitro reconstitution of this interaction using recombinantly expressed and purified intermembrane space domains of Tim50 and Tim23. We established two independent methods, chemical cross-linking and surface plasmon resonance, to track their interaction. In addition, we identified mutations in Tim23 that abolish its interaction with Tim50 in vitro. These mutations also destabilized the interaction between the two proteins in vivo, leading to defective import of preproteins via the TIM23 complex and to cell death at higher temperatures. This is the first study to describe the reconstitution of the Tim50-Tim23 interaction in vitro and to identify specific residues of Tim23 that are vital for the interaction with Tim50. © 2009 by The American Society for Biochemistry and Molecular Biology, Inc.

Journal of Biological Chemistry

Interaction of Tim23 with Tim50 is essential for protein translocation by the mitochondrial TIM23 complex

Efficient white electroluminescence (EL) is obtained from metal-oxynitride-oxide-silicon (MONOS) structures with a silicon-rich SiO 2 -SiON interface as an active layer. Samples containing only silicon show white EL under a constant current excitation of 500 μA. The EL spectra consist of three main bands associated with the neutral oxygen vacancy at 430 nm, Eδ′ centers at about 550 nm, and nonbridging oxygen hole centers peaking at 650 nm. After Gd co-doping into the SiO2:Si-nc layer, the light emitted from the MONOS structure observed by the naked eye is clearly white, but the constant current needed for the EL excitation is reduced five times. A fourfold increase in the external EL power efficiency after Gd co-doping (up to 3× 10-4 %) is observed. © 2009 The Electrochemical Society.